A preview release of NeXTSTEP (version 0.8) was shown at the launch of the NeXT Computer on October 12, 1988. The first full release, NeXTSTEP 1.0, shipped on September 18, 1989.[2] The last version, 3.3, was released in early 1995, by which time it ran on not only the Motorola68000 family processors used in NeXT computers, but also Intelx86, SunSPARC, and HPPA-RISC-based systems.

NeXTSTEP was later modified to separate the underlying operating system from the higher-level object libraries. The result was the OpenStep API, which ran on multiple underlying operating systems, including NeXT's own OPENSTEP.

Apple purchased NeXT in 1996, to use its more advanced operating system to replace Classic Mac OS, which Apple had been unable to modernize internally. Apple's OS X and iOS are direct descendants of NeXTSTEP, through the OPENSTEP lineage, and several OS X apps such as TextEdit, Mail and Chess are descended from NeXTSTEP applications.

NeXTSTEP is notable for having been a preeminent implementation of the last three items. The toolkits offered considerable power, and were used to build all of the software on the machine. Many developers found that the distinctive features of the Objective-C language made the writing of applications with NeXTSTEP far easier than on many competing systems, which made NeXTStep a paragon of computer development.

NeXTSTEP's user interface is considered to be refined and consistent. It introduced the idea of the Dock (carried through OpenStep and into OS X) and the Shelf. NeXTSTEP also created or was among the very first to include a large number of other GUI concepts now common in other operating systems: 3D "chiseled" widgets, large full-color icons, system-wide drag and drop of a wide range of objects beyond file icons, system-wide piped services, real-time scrolling and window dragging, properties dialog boxes called "inspectors", window modification notices (such as the saved status of a file), and more. The system was among the first general-purpose user interfaces to handle publishing color standards, transparency, sophisticated sound and music processing (through a Motorola 56000DSP), advanced graphics primitives, internationalization, and modern typography, in a consistent manner across all applications.

1990 CERN: A Joint proposal for a hypertext system is presented to the management. Mike Sendall buys a NeXT cube for evaluation, and gives it to Tim Berners-Lee. Tim's prototype implementation on NeXTStep is made in the space of a few months, thanks to the qualities of the NeXTStep software development system. This prototype offers WYSIWYG browsing/authoring! Current Web browsers used in "surfing the Internet" are mere passive windows, depriving the user of the possibility to contribute. During some sessions in the CERN cafeteria, Tim and I try to find a catching name for the system. I was determined that the name should not yet again be taken from Greek mythology. Tim proposes "World-Wide Web". I like this very much, except that it is difficult to pronounce in French...

Some features and keyboard shortcuts now commonly found in web browsers can be traced to NeXTSTEP conventions. The basic layout options of HTML 1.0 and 2.0 are attributable to those features available in NeXT's Text class.[4]

Altsys made a NeXTSTEP application called Virtuoso, version 2 of which was ported to Mac OS and Windows to become Macromedia FreeHand version 4. The modern "Notebook" interface for Mathematica, and the advanced spreadsheet Lotus Improv, were developed using NeXTSTEP. The software that controlled MCI's Friends and Family program was developed using NeXTSTEP.[6][7]

About the time of the 3.2 release, NeXT teamed up with Sun Microsystems to develop OpenStep, a cross-platform object-oriented API standard derived from NeXTSTEP. Implementations of that standard were released for Sun's Solaris, Windows NT, and NeXT's version of the Mach kernel. NeXT's implementation was called "OPENSTEP for Mach" and its first release (4.0) superseded NeXTSTEP 3.3 on NeXT, Sun and Intel IA-32 systems.

Following an announcement on December 20, 1996,[8] on February 4, 1997, Apple Computer acquired NeXT for $429 million. Based upon the "OPENSTEP for Mach" operating system, and developing the NeXT API to become Cocoa, Apple created the basis for OS X,[9] and eventually, in turn, for iOS.

The anime series Serial Experiments Lain was influenced by NeXTSTEP and Mac OS. References may be found throughout the show and its affiliated media, most notably the slogan for the Lain PSX Game, "Close the world, Open the NeXT".